Liquid leak detector

ABSTRACT

This invention relates to liquid leak detectors and detection systems. A liquid leak detector ( 10 ) includes a first electrically conducting layer ( 12 ), a second perforate, open, porous and/or permeable conducting layer ( 13 ) opposed to said first layer and an intermediate layer perforate, open, porous and/or permeable layer ( 14 ) for electrically isolating the two conducting layers ( 12, 13 ) whilst allowing liquid, which passes through the second conductor ( 13 ), to form an electrically conducting path between the conductors ( 12, 13 ).

[0001] This invention relates to liquid leak detectors and detectingsystems.

[0002] There have been many proposals for detecting leaks, particularlyin domestic or warehousing situations. A great many are based on systemsusing a pair of spaced probes linked to an alarm such that when acircuit is made by a liquid extending between the probes, the alarmsounds. Other proposals include float operated switches. Problems canarise with these arrangements first because they tend to cover only onelocation in a remote space; secondly because the liquid may run awayfrom the probe rather than towards it and thirdly because they tend onlyto work on or in relation to horizontal surfaces.

[0003] From one aspect the invention consists in a liquid leak detectorincluding a first electrically conducting layer, a second perforate,open and/or permeable electrical conducting layer opposed to said firstlayer and an intermediate layer perforate, open, porous and/or permeablelayer for electrically isolating the two conducting layer whilstallowing liquid which passes through the second conductor to reach thefirst conductor to form an electrical conducting path between theconductors.

[0004] In a preferred embodiment the first conducting layer is carriedon an insulating base and indeed may be a coating or film on a surfaceof that base. In this configuration it is particularly preferred thatthe base is flexible so that the detector as a whole may be flexible andmay, for example, be suitable for wrapping around pipes or the like.

[0005] In an alternative arrangement, when the pipe is metal the pipecould constitute the first conductor. In that case the intermediatelayer and second conductor could conveniently be helically wound on thepipe and covered with a further insulator. It will equally beappreciated that the pipe could be considered to constitute the secondconductor, in as much as once a leak starts the pipe is perforate.

[0006] From another aspect the invention also includes, a liquid leakdetector for use with an electrically conducting pipe of the likecomprising a perforate or open insulating layer for wrapping around thepipe and a flexible conductor for wrapping around the insulating layer.

[0007] Alternatively, the second conductor may be a sheet of metal mesh,in which case the mesh openings may be funnel shaped in cross section.Similarly, it could be a sheet of perforate metal and in that case itwould be preferred that the perforations are either funnel shaped incross section or surrounded by respective depressions. In thesearrangements liquid impinging on the detector will tend to be capturedby the openings or perforations and passed through the intermediatelayer to the first conducting layer. This is in contrast to detectorsthat use planar conductors, in which the liquid would simply run alongthe surface of the upper conductor, if it is inclined at any angle.

[0008] The intermediate layer may be a mesh or perforate plate, or itmay comprise a plurality of formations formed on the first conductinglayer. In another arrangement it may be a plurality of spaced ridges. Inany of these cases the intermediate layer may be physically distinctfrom the other layers, or it may be printed or moulded on the firstconducting layer. In this case it would typically be formed from acurable polymer. In its mesh form, the intermediate layer mayconveniently be made of nylon. In a still further embodiment theintermediate layer may be formed by protrusions on the insulating basethat extends through the conducting layer. For example, for smalldetectors it may be desirable to etch ridge formations into asemi-conductive base, metalise the surfaces in between the ridges andthen position the second conducting layer on top.

[0009] In general it will be desirable to make the intermediate layer ofhydrophobic material so that the liquid will be readily passed throughto the first conductor to create rapid triggering, but in some uses,particularly where the detector may be above the leak, for example inpipe wrapping, a porous intermediate layer may be preferable. Forexample a wadding layer could be used to wick the liquid through, butsuch an arrangement is likely to be less sensitive.

[0010] The invention also includes a detection system where detectorsare formed for specific zones so that the location of a leak can beidentified. In the pipe arrangement this can be particularlyconveniently achieved by wrapping the second electrode in individuallengths and connecting a transmitter to a further conductor so that whenthe leak path is made by leaking liquid, the transmitter is turned onand an encoded signal is sent to an alarm station, which can identifythe respective transmitter of the zone.

[0011] It is desirable to form liquid barriers between the zones andthis could be done by injecting sealant through the mesh at the zoneboundaries, wrapping flexible tape, e.g. PTFE tape, around the meshes atthe zone boundaries so that the meshes are compressed, or encircling themeshes at the boundaries with a ring or grommet. Alternatively a ring orgrommet could simply be placed on the pipe, but that would preclude theinsulator mesh being wrapped as a continuous layer.

[0012] In a further alternative, which would most usually be used for agenerally planar detector, the first conductor may itself be a mesh sothat liquid can pass right through the detector. This introduces thepossibility of a reservoir, for example a drip tray, being placedbeneath the detector to capture leaking liquid so that damage does notoccur, before the alarm is reacted to. This is particularly suitable fordetectors placed under, for example, water tanks, dishwashers andwashing machines. The tray or reservoir could be formed from aluminium,very much in the manner of a disposable cooking tray.

[0013] The invention also includes a detection system including at leastone detector as defined above. In that case an alarm or indicator may beconnected in series with the first and second conductors such that theelectrical paths set up by the liquid completes a circuit. The flow ofliquid may be used to turn on or off a suitably connected transistor Analarm may be proved for each detector so that the location of a leak canbe indicated.

[0014] Although the invention has been defined above, it is to beunderstood that it includes any inventive combination of the featuresset out above or in the following description. The invention may beperformed in various ways and specific embodiments will now bedescribed, by way of example, with reference to the accompanyingdrawings in which:

[0015]FIG. 1 is a scrap vertical section through a detector;

[0016]FIG. 2 is an exploded view of the detector of FIG.

[0017]FIG. 3 is a circuit diagram of a detection system;

[0018]FIG. 4 illustrates a part of an alternative embodiment;

[0019]FIG. 5 is a schematic view of a FIG. 1 type arrangement, butshowing an additional mesh insulating layer;

[0020]FIG. 6 is an alternative construction of the FIG. 5 arrangement;

[0021]FIG. 7 is a diagrammatic view of a detection system incorporatingzone detection;

[0022]FIG. 8 is an alternative form of a detection system of FIG. 7 andis suited for forming a zone array on a generally flat surface;

[0023]FIG. 9 illustrates an alternative zone detection system, whichcould also constitute a stand alone detector;

[0024]FIG. 10 illustrates yet a further zone detection system; and

[0025] In FIG. 1 a detector, generally indicated at 10, includes aninsulating base 11 on the upper surface of which is an electricallyconducting layer 12; a conducting mesh 13 and an intermediate insulatormesh 14. In use the conducting layers 12 and 13 are connected in serieswith a piezoelectric sounder 15 and a battery 16 so that when impingingwater creates an electrical path 17 the sound of 15 gives an alarm.

[0026] The structure shown has a number of surprising advantages. Firstthe use of the open meshes 13 and 14 mean that any liquid, e.g. water,which impinges on the conducting layer 13 tends to be locally trapped bythe mesh openings 18 and then quickly passes through the mesh 14 to theconducting layer 12 setting up an electrical path 17. In order to stopexcessive wetting, which may tend to restrict the flow of water down tothe lower plate, the intermediate layer 14 is preferably made with ahydrophobic material. It is particularly preferred that the openings 18may be formed with a funnel cross section as illustrated at 18 a.

[0027] An alternative structure is schematically indicated in FIG. 2 at19. Here perforations 20 have been punched in a metal plate so thatsurrounding depressions 21 are formed, which will again encourage waterflow down through the plate 13 rather than along the surface of theplate.

[0028] As has already been described many variations on thisconstruction may be utilised. The layer 12 may be an evaporated coatingon the insulating base 15, in another embodiment, or it may be a foillayer adhered to it. The insulating base 13 may be flexible, for exampleit may be a neoprene type material and this would be particularlysuitable if the detector was to be wrapped around a pipe, because itwould also have a thermally insulating function.

[0029] The insulating layer 14 could be formed by printing or moulding apolymer on the conducting layer 12 and need not necessarily be in theform of a mesh, but could for example, as shown in FIG. 4 be formed by aseries of ridges 22.

[0030] The mesh layer 13 could be covered by a further insulating meshlayer to reduce the risk of short circuits (for example if the detectoris being wrapped on a metal surface), whilst still allowing liquid flow.With the pipe wrap arrangement wherein the solid electrode is remotefrom the pipe surface the detector is likely to contain the leak atleast for a period. Further impedance measurement techniques may beutilised to locate the position of the leak relative to a datumposition. AC or DC voltage may be used.

[0031] Turning to FIG. 4, it will be seen that an additional mesh 23 isprovided over the conductor 13 as will be appreciated by a personskilled in the art, this is required where the detector engages againsta conducting vessel or pipe.

[0032]FIG. 6 shows substantially the same arrangement, but here thefirst conducting layer 12 has been rendered as a mesh so that liquid canpass right through the detector and the base plate 11 has been replacedby a spaced drip tray 24 for containing liquid to allow at least aperiod whilst damage will not occur after the alarm has sounded. Thismight be particularly useful in an automated system, in which a controlmodule closed off valves to prevent further egress of liquid from theleak.

[0033] Turning to FIG. 7, it will be seen that a detector systemgenerally indicated at 25 essentially consists of a series of detectionzones or sections, examples of which are shown at 26 and 27. A detectorof the type generally described is formed in each section, but forconvenience the insulating mesh layers 14 and 23 are continuous alongthe length of the pipe as is the conductor 12. The conductors 13 are,however, at least electrically confined to their respective zones andare conveniently wound as individual sections. A further conductinglayer 28 is wound on the insulating sheet 11 and respective transmitters29, 30 are connected between the conducting segments 13 and theconductor 28. The conductors 12 and 28 are connected through an alarmmodule 31 in such a way that when the conductors 13 and 11 are connectedby a leaking liquid the transmitters 29 are turned on and feed a signalto an alarm 32 and an alarm indicator 33, whereby the alarm 32 issounded and the indicator 33 discriminates a unique coded signal fromthe alarm in the leaking zone to indicate the location of the leak.Liquid barriers are preferably formed at the zone boundaries 34, forexample by the mechanisms identified above or the clamps describedbelow.

[0034]FIG. 8 illustrates an alternative zone detection system in which atrigger circuit 35, for each zone is connected between an electricallyfloating solid conductor 12 and a negatively biased solid conductor 28.When water penetrates the insulating mesh 14 the floating conductor 12is taken up to the positive rail voltage of conductive mesh 13. The fullvoltage drop causes the respective circuit 35 to trigger creating asignal at the central alarm indicator 33.

[0035] It will be noted that each zone may be in the form of a pad andthe pads may form an array on a generally flat surface.

[0036] In FIG. 9 a similar circuit is shown but here the trigger circuitis used to trigger a normally inoperative circuit 36, which may, forexample, generate a uniquely coded signal.

[0037]FIG. 10 illustrates a particular example of FIG. 8 in which anintegrated circuit acts as the trigger circuit 35 and is used togenerate a unique identification signal for the leaking zone, which canthen set off an appropriate alarm or inform monitoring software. Herethe integrated circuit is connected between an electrically floatingmesh 13 and a negative conductor 28, with the solid conductor 12 beingpositive, so that the mesh 13 is taken up to this positive rail voltageby water extending between 13 and 12.

[0038] In addition, there is a cover mesh 23, for the conductor 13 andsolid insulating outer layer 11, an insulating layer 27 between theconductors 12 and 28, and an insulating mesh layer 38 between conductors13 and 12.

[0039] In certain situations, for example it a leak detector is placedunder a shower tray, condensation may be routinely present. It would bedesirable in such circumstances, to ensure that the detector was not setoff by condensation and this can be achieved by increasing the pathlength between the conductor 13 and the conductor 11. If the path lengthis over a certain distance, then individual drops of water will notpenetrate, but more continuous leaks will form a liquid path between theconductors causing an alarm to sound. Conveniently the increased pathlength can be achieved by wrapping additional mesh layers between theconductors. In the embodiments built by the applicants, a wrapping ofthree mesh layers has been sufficient to discriminate betweencondensation and a leak. Each layer of mesh is nominally 0.75millimetres thick.

[0040] FIGS. 11(a) and (b) illustrate a two part ring 39 which can beclamped around the pipe to form the waterproof barrier between zones. Atits simplest form it comprises, for example, two C-shaped rubber orplastic elements 40 clamped at their free ends around the pipe.Conveniently, however, those conductor elements, which are electricallycontinuous along the length the detector system 25 may be electricallyconnected through the elements 40 as illustrated in FIG. 11b at forexample 41. FIG. 11 illustrates a clamp configured for use with the FIG.10 system. The outer sheath 42, of an element 40 may contain the triggercircuit 35.

1. A liquid leak detector including a first electrically conductinglayer, a second perforate, open, porous and/or permeable conductinglayer opposed to said first layer and an intermediate layer perforate,open, porous and/or permeable layer for electrically isolating the twoconducting layers whilst allowing liquid, which passes through thesecond conductor, to reach the first conductor to form an electricalconducting path between the conductors.
 2. A detector as claimed inclaim 1 wherein in the first conducting layer is carried on aninsulating base.
 3. A detector as claimed in claim 2 wherein the firstconducting layer is a coating or film on the surface of the base.
 4. Adetector as claimed in any one of the preceding claims in which thesecond conductor is a sheet of metal mesh.
 5. A detector as claimed inclaim 4 wherein the mesh openings are tunnel shaped in cross-section. 6.A detector as claimed in any one of Claims wherein the second conductinglayer is a sheet of perforate metal.
 7. A detector as claimed in claim 6wherein at least some perforations are surrounded by respectivedepressions.
 8. A detector as claimed in any one of the preceding claimswherein the intermediate layer is a mesh.
 9. A detector as claimed inany one of claims 1 to 7 wherein the intermediate layer is a perforateplate.
 10. A detector as claimed in any one of claims 1 to 7 wherein theintermediate layer comprises a plurality of formations formed on thefirst conducting layer.
 11. A detector as claimed in claim 10 whereinthe intermediate layer comprises a plurality of spaced ridges.
 12. Adetector as claimed in any one of the preceding claims wherein theintermediate layer is printed or moulded on the first conducting layer.13. A detector as claimed in claim 2 wherein the intermediate layer isformed by protrusions on the insulating base that extend through theconducting layer.
 14. A detector substantially as hereinbefore describedwith reference to the accompanying drawings.
 15. A detection systemincluding at least one detector as claimed in any one of the precedingclaims.
 16. A system as claimed in claim 15 including an alarm orindicator connected in series with the first and second conductors suchthat the electrical path set up by the liquid completes the circuit. 17.A system as claimed in claim 15 including a trigger circuit connectedbetween the first and second conductors, which is activated when anelectrical path is formed when the liquid interconnects the first andsecond circuits.
 18. A system as claimed in claim 16 or 17 wherein thereis an alarm or trigger for each detector.
 19. A detection system asclaimed in any one of claims 15 to 18 including a waterproof barrierlocated between the zones.
 20. A detection system as claimed in claim 19wherein at least one conductor is electrically continuous through thezone.